Pulse width modulation is widely used in Digital-to-Analogue (D-A) conversion. In order to convert a series of digital values into analogue form using pulse width modulation, the digital values are used to modulate the widths of a stream of pulses, which is then low-pass filtered to produce a continuously varying analogue signal. Such a technique is widely used in voice applications to generate an analogue voice signal from a series of digital values. Such D-A conversion using pulse width modulation can be performed in hardware (requiring a hardware PWM generator incorporating a hardware timer) or software (requiring a hardware timer under software control).
It is often necessary to generate a plurality of (channels of sound. Conventionally, to generate a plurality of sound channels in hardware requires a dedicated hardware PWM generator (with its hardware timer) for each channel. Although such an approach requires minimal software control, it is expensive to produce in integrated circuit form since the circuit area required is proportional to the number of channels/PWM generators needed. Conventionally, to generate a plurality of sound channels in software still requires a dedicated hardware timer for each channel, and an additional hardware timer for overall PWM system operation. Although such an approach involves moderate software control, and requires less circuit area than the previously discussed hardware implementation, it is expensive to produce in integrated circuit form since the circuit area required is still highly dependent on the number of channels/hardware timers needed.
It is an object of this invention to provide an arrangement and method for producing a plurality of pulse width modulated signals, which can be implemented largely in software, and in which the above disadvantages may be alleviated.